[tests/conftest.py]: new API runcmd_interactive.

Changes:
-- new API runcmd_interactive to execute a command in interactive mode.
Usage: Say in a Test, we want to run "config save" and want to pass
confirmation later.

Signed-off-by: Praveen Chaudhary <pchaudhary@linkedin.com>

tests/conftest.py

@@ -555,6 +555,19 @@ def runcmd(self, cmd: str) -> Tuple[int, str]:
 
         return (exitcode, out)
 
+    def runcmd_interactive(self, cmd):
+        res = self.ctn.exec_run(cmd, socket=True, stdout=True, stdin=True, tty=True)
+        try:
+            exitcode = res.exit_code
+            out = res.output
+        except AttributeError:
+            exitcode = None
+            out = res
+        if exitcode is not None:
+            print "-----rc={} for cmd {}-----".format(exitcode, cmd)
+
+        return (exitcode, out)
+
     # used in buildimage tests, do not delete
     def copy_file(self, path: str, filename: str) -> None:
         tarstr = io.BytesIO()