fix time parsing for scheduled maintenance events

[bwagner5]

Issue #, if available:
#147

Description of changes:
Fix bug where scheduled maintenance events times were parsed wrong. This would cause scheduled event handling to fail when the date of the start or end time was a 1 digit day. We were assuming the day digit would always be padded with a 0 to make it two digits.

Updated the test and date parsing string.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #148 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #148   +/-   ##
=======================================
  Coverage   95.16%   95.16%           
=======================================
  Files           8        8           
  Lines         620      620           
=======================================
  Hits          590      590           
  Misses         18       18           
  Partials       12       12           

Impacted Files	Coverage Δ
pkg/interruptionevent/scheduled-event.go	93.33% <ø> (ø)

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