Make sure $ characters are not interpreted by shell.

fix #27

modoboa_installer/scripts/modoboa.py

@@ -73,7 +73,7 @@ class Modoboa(base.Installer):
             "--timezone", self.config.get("modoboa", "timezone"),
             "--domain", self.config.get("general", "hostname"),
             "--extensions", " ".join(self.extensions),
-            "--dburl", "default:{0}://{1}:{2}@{3}/{1}".format(
+            "--dburl", "'default:{0}://{1}:{2}@{3}/{1}'".format(
                 self.config.get("database", "engine"), self.dbname,
                 self.dbpasswd, self.dbhost)
         ]
@@ -81,7 +81,7 @@ class Modoboa(base.Installer):
             args = ["--devel"] + args
         if self.config.getboolean("amavis", "enabled"):
             args += [
-                "amavis:{}://{}:{}@{}/{}".format(
+                "'amavis:{}://{}:{}@{}/{}'".format(
                     self.config.get("database", "engine"),
                     self.config.get("amavis", "dbuser"),
                     self.config.get("amavis", "dbpassword"),