BUG: Fixed exclusion list

Currently iris test coding standards will perform pep8 checks on files
contained within the build directory and then ignore the results.  This
commit removes this checking entirely and fixes a bug present in
generating the assumed directory for the iris repository from the iris
path (a problem which arises when considering softlink vs real paths).
UM/CF metaRelate code and map format changes.
UM/CF metaRelate map data changes.
Added missing UM/CF translations.
Refactor of GRIB/CF map.
Fallback to REAL constants where necessary.

For FieldsFile fields with no BDX, BDY and no X, Y vectors,
use the values in the file's REAL_CONSTANTS section instead.
Add abstract definitions
Comment and test name tweaks
Push regular_x/y methods to superclass
Revert handling of horiz_grid_type
name to grib
review actions
Fix typo and tweak test name
Use ubuntugis stable.
Merge pull request #857 from bjlittle/travis_gdal_fix

Switch to ubuntugis stable.
Merge pull request #844 from rhattersley/ff-no-coords

Fallback to using REAL_CONSTANTS.
Merge pull request #835 from bblay/name_to_grib

name to grib
Merge pull request #852 from bjlittle/refactor_grib_cf_map

Cosmetic reformat of GRIB/CF map.
Reorder GRIB/CF map entries.
Merge pull request #842 from bjlittle/um_cf_map

Ingest MetaRelate generated UM/CF mappings.