tools: Exclude testing and benchmark files from coverage

[shahzadlone]

Ignores testing and benchmark files that don't need to included in the code coverage report.

[codecov]

Codecov Report

Merging #280 (c303cf5) into develop (2a32f05) will increase coverage by 4.09%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #280      +/-   ##
===========================================
+ Coverage    58.28%   62.37%   +4.09%     
===========================================
  Files          103       84      -19     
  Lines        10200     9245     -955     
===========================================
- Hits          5945     5767     -178     
+ Misses        3622     2871     -751     
+ Partials       633      607      -26     

Impacted Files	Coverage Δ
bench/collection/utils.go
db/tests/utils.go
db/tests/query/commit/utils.go
db/tests/query/all_commits/utils.go
bench/storage/utils.go
db/tests/query/one_to_two_many/utils.go
db/tests/query/simple/utils.go
db/tests/query/one_to_one/utils.go
db/tests/mutation/inline_array/utils.go
db/tests/query/complex/utils.go
... and 9 more

[AndrewSisley]

Looks good, cheers. Bit of a shame it excludes packages that have no tests still (e.g. CLI), but that is a problem for another day :)