Split and refactor querying for total CI builds

This MR:
- splits metrics for builds in `running` state just like for the `pending` state (so projects are distinguished by`shared_runners_enabled` value),
- refactors querying for metrics about total builds count, so the data is collected with one query instead of two.

/fyi @ayufan

See merge request !30

This reverts commit 3c28bd41.

Add another CI Builds related metrics

This MR adds some CI Builds metrics:

- number of builds in `running` state, that were not updated since more than last hour,
- number of builds in `pending` state, that are created for projects with `shared_runner_enabled` set to `true`,
- number of builds in `pending` state, that are created for projects with `shared_runner_enabled` set to `false`,

```
ci_builds_stale{status="running",when="last_hour"} 2
ci_builds_total{status="pending",shared_runners_enabled_projects="1"} 5
ci_builds_total{status="pending",shared_runners_enabled_projects="0"} 2
```

MR is prepared on top of !27.

Related to gitlab-org/gitlab-ce#23366.

/cc @ayufan @ahmadsherif

See merge request !29

Add basic metrics for CI Builds

This MR adds basic metrics for CI Builds. Currently there is a support for:

- number of all builds (works for CE and EE)
- number of builds executed per runner (works for CE and EE)
- number of builds executed per runner for mirrored projects (works for EE, returns `0` on CE)

Output looks like:
```
ci_builds_total{status="running"} 0
ci_builds_per_runner{status="running",runner="8",mirrors="0"} 0
ci_builds_per_runner{status="running",runner="8",mirrors="1"} 0
ci_builds_per_runner{status="running",runner="9",mirrors="0"} 0
ci_builds_per_runner{status="running",runner="9",mirrors="1"} 0
```

References gitlab-org/gitlab-ce#23366

/cc @ayufan

See merge request !27

Use a Lua script to calculate queue stats

cc/ @pcarranza

See merge request !28

Closes #8

Faster tests because of caching

See merge request !22

Remove soft deleted namespaces

This query yields 0 each time now, and old ones got nukes.

See merge request !26

This query yields 0 each time now, and old ones got nukes.

Business stats

Refactoring and moooooooar queries

See merge request !24

Before this commit, the queries totalled at about a minute execution
time, now this is brought down to about 2 seconds.

Add a prober for git processes

cc/ @pcarranza

See merge request !25

Using the previous commit I was able to come up with a couple more
queries. The ordering is on table name, so the index don't have to be
swapped hopefully.

In the previous version it was harder to extend as you could forget to
include your symbol in the query list. Also, the queries had some
duplication. For extensions this is the easier way forward and the
DRYest.

Also added the first tests for database monitoring.

Update queries for better monitoring

See merge request !23

Add ability to query row counts

This commit allows for queries which only request for row counts to be
gathered and written for Prometheus to gather.

At this time 3 simple queries are added which monitor how many projects
are orphaned and/or pending_delete, though the structure of the code
allows for easily adding more queries which do
SELECT COUNT(<whatever>) FROM <whatever>;

See merge request !21