fix to work SpyOn in Jasmine

[knight9999]

Platforms affected

All platforms. But tests only

What does this PR do?

At the Cordova-Common 3.1.0, the logger[level] property becomes not writable. (level = results, verbose, normal, warn, info, error)
Then we can't use SpyOn for logger[level] in jasmine tests.

Actually npm run tests fails like

    Error: <spyOn> : results is not declared writable or has no setter
    Usage: spyOn(<object>, <methodName>)

To resolve this issue, this PR overrides CordovaLogger.prototype.addLevel method in test code (i.e. cli.spec.js) to make logger[level] property writable.

What testing has been done on this change?

npm run test

Checklist

• Reported an issue in the JIRA database
• Commit message follows the format: "CB-3232: (android) Fix bug with resolving file paths", where CB-xxxx is the JIRA ID & "android" is the platform affected.
• Added automated test coverage as appropriate for this change.