Add event for snapshotting in progress

[zhucan]

Signed-off-by: zhuc [email protected]

What type of PR is this?

/kind feature

What this PR does / why we need it:
Need to add an event on the VolumeSnapshot API object after we've created VolumeSnapshotContent in the common controller

Which issue(s) this PR fixes:

Fixes #268

Special notes for your reviewer:
@xing-yang

Does this PR introduce a user-facing change?:

Add event for snapshotting in progress

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[xing-yang]

/lgtm
/approve

[yuxiangqian]

this needs rebase as a bug fix has been recently checked-in. :(. @zhucan

[xing-yang]

@zhucan please rebase.

[zhucan]

@xing-yang @yuxiangqian done

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xing-yang, zhucan

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