[RFE] azure-init should send its version as part of User-Agent string for IMDS request

[anhvoms]

Current situation

Currently azure-init is sending the User-Agent string "azure-init test" when making imds query. azure-init should be sending the its version (e.g., "azure-init v0.1.1") for released binary and it should be sending the commit hash appended to existing version during nightly test.

Impact

This allows easy troubleshooting and correlation by using platform telemetry. It will help us quickly narrow down which version of azure-init has issues etc...