Add timestamp tests

[mapedraza]

• 1. Add explicitAttrs value = [ ]
     Expected value = no update to CB entity
  • 1.a Using timestamp = true (it also skips TImeInstant Attr)

    iotagent-node-lib/test/functional/testCases.js

    Line 1707 in 3946928

    // 0400 - TIMESTAMP TESTS

  • 1.b Using timestamp = false
• 2. Add timestamp = false, TimeInstant is defined by a JEXL attribute expression and explicitAttrs value = [ attrA ]
     Expected value = no TImeInstant value present, only attrA

CC: @danielvillalbamota

[fgalan]

Test added in PR #1605