Add a compliance check that tries to load MAINTAINERS.yml with
get_maintainer.Maintainers() if it's been modified by the CL, and fail
compliance if it fails to be parsed.
Example output:
```
ERROR : Test MaintainersFormat failed:
Error parsing MAINTAINERS.yml: MAINTAINERS.yml: YAML error: while
scanning a simple key
in "MAINTAINERS.yml", line 976, column 1
could not find expected ':'
in "MAINTAINERS.yml", line 977, column 3
```
```
ERROR : Test MaintainersFormat failed:
Error parsing MAINTAINERS.yml: MAINTAINERS.yml: glob pattern
'drivers/regulator' in 'files' in area 'Drivers: Regulators' matches a
directory, but has no trailing '/'
```
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
f33d43795d