ALLJOYN-1570 cmtest unit test can be built without building alljoyn_core

When building cmtest the SConscript would use the alljoyn library.  These
changes will cause the library to be built using a library that was built using
only code from common.  The one exception is that Status.h and Status.cc are
built using the information found in alljoyn_core and common.  This is required
since we only have one status.h file.  If we want to eliminate even the Status
codes from alljoyn_core we can build the common project from common.  The
new SConstruct file will define a build variable BUILD_COMMON_STATUS and will
create a Status.h and Status.cc.

The common project currently only produces object files and the unit test
cmtest.  If common is build from the common project the aside from the object
files the only new folder that will be created will be a test folder that
contains the cmtest executable.

While making these changes it was discovered that BufferedSink.cc and
IODispatch.cc were using status codes from alljoyn_core.  BufferedSink was
using ER_PACKET_TOO_LARGE this was replaced with a common status code
ER_BUFFER_TOO_SMALL.  IODispatch User ER_BUS_STOPPING none of the existing
status codes seemed appropriate to replace this status so a new status code
was created ER_IODISPATCH_STOPPING.

Change-Id: I1398a27744b40d9e3006e10ad410390749d9194c