Initial snmp agent integration
Basic agent to manager communication working
Add terminate callback to exometer report plugins.

Also snmp is only started if the export is configured to be enabled.
Move main exometer eunit test to CT.

Also adds skeleton for snmp test suite.
Removed old unused tests
Add SNMP startup configuration tests
Working agent-manager communication tests

Exometer won't start the SNMP application anymore implicitely. The user
is required to properly configure and start SNMP in its node when
trying to use SNMP export in exometer.
Add exometer snmp compiler process.

Includes API to load a MIB from disk and return its abstract form.
Preliminary abstract mib format loading
Using textual mib template for dynamic mib creation.
Working MIB generation for enabling and disabling metrics.
Improving test suites for automatic testing

- Making tests compatible to R15 releases
- Show raw log output upon failed tests.
- Don't fetch deps in travis ci again
- Skipping distributed tests on travis since ct_slave doesn't work on
  travis
Add SNMP export for simple counters and fast counter.

Includes the test test_counters_get in exometer_snmp_SUITE to
illustrate how counters can be read through a SNMP manager.

Known caveats which are fixed later:

- does only work with OTP R16B01 and up
- does only work for counter datapoint 'value'
Refactoring all SNMP support into exometer_report_snmp

Further tests were fixed to run on all supported OTP versions.
Merge pull request #11 from Feuerlabs/tb-snmp-support

SNMP export support for Exometer metrics