fix proxy run to support single and double quotes

Signed-off-by: endika <[email protected]>

charms/osm/sshproxy.py

@@ -367,7 +367,7 @@ def run(self, cmd: str) -> (str, str):
         expect it not to.
         """
         if isinstance(cmd, str):
-            cmd = shlex.split(cmd)
+            cmd = shlex.split(cmd, posix=False)
 
         host = self._get_hostname()
         user = self.username