Action registration should use same validations as API
Refactor fixtures
Add test case for catching schema issues in action
Update CHANGELOG
Swap order of API object validation and model conversion
Add iequal operator for performing case-insensitive equality check on strings.
Add new criteria comparision operators:

- contains
- icontains
- ncontains
- incontains
Add tests for new operators.
Use better argument names - v1 and v2 are ambigious and it's not clear which
argument is value and which one is pattern.
Use keyword arguments so it's more clear what is going on.
Improve rules criteria documentation and document all the available operator
types.
Update changelog.
Fix bug in action update during registration
Fix lint.
Update register-content.py script to default to registering nothing and update
st2ctl reload command to pass --register-sensors --register-actions flags to the
command if user doesn't specify which resource to register.
Default value of 'sudo' set to False.
Runner param can be defined immutable in action

* A runner param can be declared immutable in action. In this case,
we can use the 'default' value supplied in either runner or action.
We need default to be specified in at least one place.
Fix action validation regarding immutability and default values

* Default value for a runner param made immutable in either
runner or action can also come from either.
Fix packs in st2 repo.
Add test cases