Capirca correct keyword for fragment is confused and is-fragment doesn't work for Cisco targets

[mpenning]

The online docs say that is-fragment is a valid option value for Cisco rules, but I get the following error when I use is-fragment for Cisco ACLs under Capirca=1.122:

Traceback (most recent call last):
  File "test_cisco_acl.py", line 37, in <module>
    cisco_acl = Cisco(pp, exp_info=0)
  File "/opt/virtual_env/py37_test/lib/python3.7/site-packages/capirca/lib/aclgenerator.py", line 325, in __init__
    raise UnsupportedFilterError('\n %s' % '\n'.join(all_err))
capirca.lib.aclgenerator.UnsupportedFilterError:
 test-deny-ip-fragments contains unsupported keywords (is-fragment) for target cisco in policy

The online docs say is-fragment is the proper keyword, but cisco.py seems to only recognize fragments option... What's more, the Juniper unit tests use is-fragment in the Term while the Cisco unit tests use fragments in the Term. For all the obvious reasons, we need to make the fragment keyword consistent for all targets.

Test script to reproduce...

from capirca.lib.policy import ParsePolicy
from capirca.lib.naming import Naming

from capirca.lib.cisco import Cisco

defs = Naming()
defs.ParseServiceList([
    'SVC1 = 80/tcp 443/tcp',
    'SVC2 = 25/tcp',
    'ALL_SVC = SVC1 SVC2',
    ])
defs.ParseNetworkList([
    'LAN1 = 172.16.1.0/24',
    'LAN2 = 172.16.2.0/24',
    'LAN = LAN1 LAN2',
    ])

## Reproduce problem with `option:: is-fragment` for Cisco targets
acl ="""
header {
  comment:: "Demo of capirca acl DSL"
  target:: cisco ACL_IN extended
}
term test-deny-ip-fragments {
  option:: is-fragment
  action:: deny
}
term allow-to-lan {
  destination-address:: LAN
  protocol:: tcp
  source-port:: ALL_SVC
  action:: accept
}
"""

pp = ParsePolicy(acl, defs)
cisco_acl = Cisco(pp, exp_info=0)
print(cisco_acl)