Print meaningul error when invalid target specified and exit

Also adjust test_help accordingly.

Change-Id: Ib209e60937599604cdc60d06199a967aeab8ea11
Fixes-bug: #1309097

solumclient/solum.py

@@ -216,9 +216,10 @@ def main():
     try:
         parsed, _ = parser.parse_known_args()
         resource = parsed.resource
-    except Exception as se_except:
+    except Exception:
+        print("Invalid target specified to act upon.\n")
         parser.print_help()
-        return se_except
+        sys.exit(1)
 
     if resource in resources:
         try:

solumclient/tests/test_solum.py

@@ -95,12 +95,11 @@ class TestSolum(base.TestCase):
             '.*?^optional arguments'
 
         ]
-        for argstr in ['--help', 'help']:
-            help_text = self.shell(argstr)
-            for r in required:
-                self.assertThat(help_text,
-                                matchers.MatchesRegex(r,
-                                                      self.re_options))
+        help_text = self.shell('--help')
+        for r in required:
+            self.assertThat(help_text,
+                            matchers.MatchesRegex(r,
+                                                  self.re_options))
 
     # Assembly Tests #
     @mock.patch.object(assembly.AssemblyManager, "list")