Create a separate log package

[farshidtz]

This PR adds a separate logging package with extended functionality.

It:

• fixes Add logging functions with string formatting #24
• fixes Redundant snap name input #12
• fixes Warn function logs as syslog error #29

Test by adding the following to go.mod:

replace github.com/canonical/edgex-snap-hooks/v2 => github.com/farshidtz/edgex-snap-hooks/v2 da083736dcb18258dd425431d06df0b42e96760c

Add to configure hook:

log.SetComponentName("configure")
log.Infof("info testing new library")
log.Debugf("debug testing new library")
log.Warnf("warn testing new library")
log.Errorf("err testing new library")
log.Errorf("err testing new library 2")
os.Exit(1)

Build and install. Logs should show:

$ sudo snap install --dangerous ./edgex-device-mqtt_2.2.0-dev.9_amd64.snap 
error: cannot perform the following tasks:
- Run configure hook of "edgex-device-mqtt" snap if present (run hook "configure": 
-----
edgex-device-mqtt.configure: err testing new library
edgex-device-mqtt.configure: err testing new library 2
-----)

$ journalctl -f | grep "new library"
Mar 10 10:39:54 farshid-cirrus7 edgex-device-mqtt.configure[59291]: info testing new library
Mar 10 10:39:54 farshid-cirrus7 edgex-device-mqtt.configure[59291]: warn testing new library
Mar 10 10:39:54 farshid-cirrus7 edgex-device-mqtt.configure[59291]: err testing new library
Mar 10 10:39:54 farshid-cirrus7 edgex-device-mqtt.configure[59291]: err testing new library 2
Mar 10 10:39:54 farshid-cirrus7 snapd[1349]: edgex-device-mqtt.configure: err testing new library
Mar 10 10:39:54 farshid-cirrus7 snapd[1349]: edgex-device-mqtt.configure: err testing new library 2

[farshidtz]

Added more testing instructions.

[siggiskulason]

LGTM. Excellent, good to have those variable argument functions instead of needing to create a string.

[MonicaisHer]

@farshidtz Thanks a lot. Please see the inline comments.

[farshidtz]

Thanks for the reviews. I removed the option to turn on debug via environment variable because it was very hard to make it usable since snap options are persisted and override env vars by convention. Allowing both would have just made things very confusing for the user and tests.