[engine] Poor error reporting while resolving namespace

[Ekaterina Chernova]

The application class contains the following line

 - $._environment: $.find(std:Environment).require()

But std namespace is not defined at namespaces section:
Namespaces:
  =: io.murano.apps.apache
  res: io.murano.resources
  sys: io.murano.system

Deployment failed with message Unable to run find.

It will be better to add information, where the function was searched and what namespaces exist.

[Rohini Choudhary (enthurohini)]

Please specify where does this application class is defined?

[Ekaterina Chernova (efedorova)]

It's just an example. I've updated the description

[Ekaterina Chernova (efedorova)]

To reproduce whole class definition may consist of:

Namespaces:
  =: io.murano.apps.apache

Methods:
  initialize:
    Body:
      - $._environment: $.find(std:Environment).require()

[Kirill Zaitsev (kzaitsev)]

We can make the message like this:
"Unable to find function 'find' in any of loaded namespaces (list of namespaces here)"

Since we can't know which namespaces actually can exist — there is no way we can instruct someone to add 'std' or other namespace.

[Stan Lagun (slagun)]

what we can do is to catch attempts to use prefixes that were not defined and report it correctly. That is low-hanging-fruit

[Rohini Choudhary (enthurohini)]

I have tried to reproduce the bug and deploymnet get failed with error `[exceptions.KeyError]: 'Unknown namespace prefix <unknown prefix>'`. In addition, list of available namespaces can be provided only. Although current error is also sufficient to debog the problem.