scylla_node: no need to _wait_no_pending_flushes

The flush api is synchronous and so it waits for
the respective flush to get done and will return
and error if flush failed for any reason and
this will propagate through nodetool flush.

_wait_no_pending_flushes may fail if there
are spontanuous flushes, and it also tends to
timeout in nodetool cfstats in debug mode,
see for example:
https://jenkins.scylladb.com/view/master/job/scylla-master/job/dtest-debug/250/testReport/alternator_ttl_tests/TestAlternatorTTL/Run_Dtest_Parallel_Cloud_Machines___FullDtest___full_split029___test_ttl_with_load_and_decommission/
```
../scylla/.local/lib/python3.11/site-packages/ccmlib/scylla_node.py:1320: in flush
    self._wait_no_pending_flushes(verbose=kwargs.get('verbose', True))
../scylla/.local/lib/python3.11/site-packages/ccmlib/scylla_node.py:1314: in _wait_no_pending_flushes
    if not wait_for(no_pending_flushes, timeout=wait_timeout, step=1.0):
../scylla/.local/lib/python3.11/site-packages/ccmlib/common.py:675: in wait_for
    if func():
../scylla/.local/lib/python3.11/site-packages/ccmlib/scylla_node.py:1306: in no_pending_flushes
    stdout = self.nodetool('cfstats', timeout=wait_timeout, verbose=verbose)[0]
../scylla/.local/lib/python3.11/site-packages/ccmlib/scylla_node.py:754: in nodetool
    return super().nodetool(*args, **kwargs)
../scylla/.local/lib/python3.11/site-packages/ccmlib/node.py:794: in nodetool
    stdout, stderr = p.communicate(timeout=timeout)
/usr/lib64/python3.11/subprocess.py:1209: in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
/usr/lib64/python3.11/subprocess.py:2109: in _communicate
    self._check_timeout(endtime, orig_timeout, stdout, stderr)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <Popen: returncode: None args: ['/jenkins/workspace/scylla-master/dtest-debu...>
endtime = 2588.165606614, orig_timeout = 60, stdout_seq = [], stderr_seq = []
skip_check_and_raise = False

    def _check_timeout(self, endtime, orig_timeout, stdout_seq, stderr_seq,
                       skip_check_and_raise=False):
        """Convenience for checking if a timeout has expired."""
        if endtime is None:
            return
        if skip_check_and_raise or _time() > endtime:
>           raise TimeoutExpired(
                    self.args, orig_timeout,
                    output=b''.join(stdout_seq) if stdout_seq else None,
                    stderr=b''.join(stderr_seq) if stderr_seq else None)
E           subprocess.TimeoutExpired: Command '['/jenkins/workspace/scylla-master/dtest-debug/scylla/.ccm/scylla-repository/93be4c0cb0f0c53fe0eb7cd4d06ba15a7fc01d29/share/cassandra/bin/nodetool', '-h', '127.0.12.2', '-p', '7199', '-Dcom.sun.jndi.rmiURLParsing=legacy', 'cfstats']' timed out after 60 seconds
```

Signed-off-by: Benny Halevy <[email protected]>

ccmlib/scylla_node.py

@@ -1299,25 +1299,8 @@ def _write_agent_address_yaml(self, agent_dir):
     def _write_agent_log4j_properties(self, agent_dir):
         raise NotImplementedError('ScyllaNode._write_agent_log4j_properties')
 
-    def _wait_no_pending_flushes(self, wait_timeout=60, verbose=True):
-        pending_flushes_re = re.compile(r"^\s*Pending flushes:\s*(?P<count>\d+)\s*$", flags=re.MULTILINE)
-
-        def no_pending_flushes() -> bool:
-            stdout = self.nodetool('cfstats', timeout=wait_timeout, verbose=verbose)[0]
-            pending_flushes = False
-            for match in pending_flushes_re.finditer(stdout):
-                if int(match.group("count")):
-                    pending_flushes = True
-                    break
-            return not pending_flushes
-
-        if not wait_for(no_pending_flushes, timeout=wait_timeout, step=1.0):
-            raise NodeError("Node %s still has pending flushes after "
-                            "%s seconds" % (self.name, wait_timeout))
-
     def flush(self, ks=None, table=None, **kwargs):
         super(ScyllaNode, self).flush(ks, table, **kwargs)
-        self._wait_no_pending_flushes(verbose=kwargs.get('verbose', True))
 
     def _run_scylla_executable_with_option(self, option, scylla_exec_path=None):
         if not scylla_exec_path: