Add configuration to ignore certain queries

In some cases, queries may happen that we don't want to be counted by
the `make_database_queries` matcher. For example, in Rails you might get
`SHOW TABLE LIKE 'foo'` queries. These meta queries might not always be
relevant. To ignore these types of queries, you can now specify an
`ignores` configuration to DBQueryMatchers. This configuration should
consist of an array of regular expressions that when matched for a
query, will cause the query not to be counted.

Change-Id: I8f60bf2b0273be90aede52c65481a9bb75b353b7
Reviewed-on: http://gerrit.causes.com/40189
Reviewed-by: Joe Lencioni <joe.lencioni@brigade.com>
Tested-by: Henric Trotzig <henric.trotzig@brigade.com>
Namespace QueryCounter class

This class was defined in the global namespace, which makes it subject
for naming collisions. The DBQueryMatchers module is great to
encapsulate all the code for this project.

Change-Id: I21538453473c837e82bf8cb5224b2a86da20e2ed
Reviewed-on: http://gerrit.causes.com/40190
Reviewed-by: Joe Lencioni <joe.lencioni@brigade.com>
Tested-by: Henric Trotzig <henric.trotzig@brigade.com>