Fix mi-file.exp fails on remote host

This patch fixes mi-file.exp fails on remote host.  First, we can't
assume ${srcdir}/${subdir}/${srcfile} directory exists on remote host,
so this patch changes it to match ${srcfile} only on remote host.
Second, regexp pattern ".*/${srcfile}" isn't friendly to Windows path.
The file name is "basics.c" in my test env and can't match the pattern
due to "/" in it.  Remove "/" from the pattern.

gdb/testsuite:

2014-05-14  Yao Qi  <yao@codesourcery.com>

	* gdb.mi/mi-file.exp (test_file_list_exec_source_file): Don't
	match absolute path on remote host.
	(test_file_list_exec_source_files): Remove "/" from the
	pattern.