Fixes for gdb.python tests on remote Windows host.

Fixes for gdb.python tests on remote Windows host.

This patch fixes several test ERRORs and FAILs seen from running
gdb.python tests on a remote Windows host.  The problems fixed
generally fall into these categories:
- Failure to copy the .py script to the host.
- Confusion between build and host pathnames.
- Assuming pathnames printed on the host include "/" as a directory
  separator.
- Tests that need to be conditionally disabled due to missing features
  on the host, etc.

2019-08-13  Sandra Loosemore  <sandra@codesourcery.com>

	gdb/testsuite/
	* gdb.python/py-completion.exp: Download the .py file to the host
	and use its host pathname.  Conditionalize tests that use
	tab completion and manipulate files on the build machine.
	* gdb.python/py-events.exp: Download the .py file to the host
	and use its host pathname.
	* gdb.python/py-evsignal.exp: Likewise.
	* gdb.python/py-evthreads.exp: Likewise.
	* gdb.python/py-framefilter-invalidarg.exp: Match Windows
	pathname syntax.
	* gdb.python/py-framefilter.exp: Download the .py file to the right
	place on the host.  Match Windows pathname syntax.
	* gdb.python/py-mi-var-info-path-expression.exp: Download the
	.py file to the host and use its host pathname.
	* gdb.python/py-objfile-script.exp: Match Windows pathname syntax.
	* gdb.python/py-objfile.exp: Expect a host pathname, not a
	build pathname.  Skip symlink test on Windows host.  Add missing
	newline at end of file.
	* gdb.python/py-pp-maint.exp: Download the .py file to the host
	and use its host pathname.
	* gdb.python/py-pp-registration.exp: Match Windows pathname syntax.
	* gdb.python/py-section-script.exp: Use host location of binfile
	on safe-path.  Use correct path separator on Windows host.
	Reorder alternatives in gdb_test_multiple to prevent matching
	the wrong alternative on success.
	* gdb.python/py-symtab.exp: Match Windows pathname syntax.