[LNT] In command-line tool allow to use relative path for test suite location.

[vsapsai]

Summary

When test command test-suite is executed, it runs inside the sandbox and uses
test suite path as-is. So the path relative to the working directory is not
found when it is relative to the sandbox directory. Fix by converting relative
path to absolute path.

Test command nt works with relative paths correctly because it runs tests in
a different way.

lnt/trunk/lnt/tests/test_suite.py

def run_test(self, opts):
                 self._fatal("invalid --cxx argument %r, does not exist"
                             % (self.opts.cxx))
 
         if opts.test_suite_root is None:
             self._fatal('--test-suite is required')
         if not os.path.exists(opts.test_suite_root):
             self._fatal("invalid --test-suite argument, does not exist: %r" % (
                 opts.test_suite_root))
+        opts.test_suite_root = os.path.abspath(opts.test_suite_root)
 
         if opts.test_suite_externals:
             if not os.path.exists(opts.test_suite_externals):
                 self._fatal(
                     "invalid --test-externals argument, does not exist: %r" % (
                         opts.test_suite_externals,))
+            opts.test_suite_externals = os.path.abspath(
+                opts.test_suite_externals)
 
         opts.cmake = resolve_command_path(opts.cmake)
         if not isexecfile(opts.cmake):
             self._fatal("CMake tool not found (looked for %s)" % opts.cmake)
         opts.make = resolve_command_path(opts.make)
         if not isexecfile(opts.make):
             self._fatal("Make tool not found (looked for %s)" % opts.make)
         opts.lit = resolve_command_path(opts.lit)