.pytool: Avoid "is" with a literal Python 3.8 warnings in CI plugins

.pytool: Avoid "is" with a literal Python 3.8 warnings in CI plugins

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2304

To avoid SyntaxWarning with Python 3.8, change the 'is' operator
by the conventional '==' comparator.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>