Add pthread implementation for connectivity/common/umutex

Add pthread implementation for connectivity/common/umutex

Implements a pthread implementation of the u_mutex , u_cond
for platforms that can't/don't want glib.

Renames u_mutex => ca_mutex , u_cond => ca_cond

Add missing unittests.

changes u_cond_wait_until() decl because old implementation
didn't accomadate for code to handle spurious wakeups properly,
and whether condition was signaled or time expired.

Change-Id: Ibd106dad494ebac3ca85aba306f1f1fe7dcc47e2
Signed-off-by: Charlie Lenahan <charlie.lenahan@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/741
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Erich Keane <erich.keane@intel.com>