Fuel-devops dos.py show env occurs exception

The Environment.DoesNotExist exception will be generated
because django will not found corresponding model.
shell.py will be invoked by dos.py and
shell.py module gets 'env' by name which was passed through CI
where 'env' object shall be taken from settings
stored in database before.
If requested 'env' is not presented in database then
django lib throw exception but shell.py module
don't intercept it and it is root cause.

The Environment.DoesNotExist shall be intercepted
in shell.py in init function and reasonable message
shall be shown in this case.
We will be blocked to continue work with odd 'env'
which is not presented in database because 'env' is
shell.py public methods.
in this case we have to return error to CI and let to know
another processes that we was failed.

Closes-Bug: #1515258

Change-Id: I15c3e47867c5d4c168ae510110c46acde8933841

devops/shell.py

@@ -35,7 +35,12 @@ def __init__(self, args):
         self.params = self.get_params()
         if (getattr(self.params, 'name', None) and
                 getattr(self.params, 'command', None) != 'create'):
-            self.env = Environment.get(name=self.params.name)
+            try:
+                self.env = Environment.get(name=self.params.name)
+            except Environment.DoesNotExist:
+                self.env = None
+                sys.exit("Enviroment with name {} doesn't exist."
+                         "".format(self.params.name))
 
     def execute(self):
         self.commands.get(self.params.command)(self)