enable embedded compiler support for fetch histogram queries

The fetch histogram logic executes queries against the user metadata
tables HISTOGAMS and HISTORAGM_INTERVALS that require the spawning of
external arkcmp processes. The work in this check-in enables embedded
compiler for these queries so the spawning of external arkcmps is avoided.
The change introduces a "switch context" to a meta data context when
compiling the user metadata queries and "switch back" to the user context
prior to fetching the rows from the cursors on the user metadata tables.
The main change is implemented in the "readHistogram" function in
hs_read.cpp file.

A new method (switchBackContext) was added to class CmpContext class
to enable switching back to a previous context. The purpose of the new
method is to ensure that thread globals are appropriately reset when
reverting back to a previous context.

The checkin also turns OFF CQD HBASE_SERIALIZATION in file regress/tools/sbdefs
as the hbase serialization feature is not enabled yet. The feature (CQD)
was enabled during regression testing prior to this checkin.

Change-Id: Iee1b8152dee3fea0ce3d3354719b5b7aa8fb198f
Merge "enable embedded compiler support for fetch histogram queries"