CSIT-844: fix binary api rx pthread heap push/pop

CSIT-844: fix binary api rx pthread heap push/pop

We need to push/pop the rx pthread's heap without affecting other
thread(s).

Search clib_per_cpu_mheaps, locate an unused slot. Duplicate the main
thread heap pointer in that slot, and set __os_thread_index
appropriately.

Miscellaneous cleanups. Print exec_inband results as a vector, instead
of as a format string. Don't bail out of vpp_api_test with results
pending, e.g. at the end of a vpp_api_test script. Even though vpp
will eventuallly garbage-collect them, We don't want to leave
allocated reply messages lurking in the api message allocation
rings...

Change-Id: I0e8a25d1ff0d3700249dc330d079db16c2fcbc55
Signed-off-by: Dave Barach <dave@barachs.net>