Added gdb-remote stop packet expedited register tests.

Expedited registers currently checked for are pc, fp and sp.

Also broke out the gdb-remote base test case logic into
class gdbremote_testcase.GdbRemoteTestCaseBase in the new
gdbremote_testcase.py file.

TestGdbRemoteExpeditedRegisters.py is the first gdb-remote area
to be contained in its own test case class file.

The monolithic TestLldbGdbServer.py has been modified to derive
from gdbremote_testcase.GdbRemoteTestCaseBase.  Soon I will
pull out all the gdb-remote functional area tests from that class
into separate classes.

I'm intending to start all GdbRemote test cases with GdbRemote
so it is easy to run them all with a -p pattern match on the
test run infrastructure.

Also scanned and removed all cases of whitespace-only lines in
the files I touched.