tests/eas/hmp_parity: cache the trappy.FTrace object in OffloadMigrationAndIdlePull
tests/eas/hmp_parity: cache the trappy.FTrace object in OffloadMigrationAndIdlePull

In the OffloadMigrationAndIdlePull test we call SchedMultiAssert
multiple times with the trace filename as a parameter, making
each SchedMultiAssert create a trappy object for itself.

Call trappy.FTrace from the test itself so that we can pass a reference
to it to all the SchedMultiAssert invocations, avoiding multiple copies
of effectively the same thing.

joelagnel/lisa,ARM-software/lisa,mdigiorgio/lisa,arnoldlu/lisa,bjackman/lisa,joelagnel/lisa,mdigiorgio/lisa,ARM-software/lisa,ARM-software/lisa,arnoldlu/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa,bjackman/lisa,credp/lisa