Throw exception when embeddingDirectory not present and not created

[aravinder111]

Check if embeddingDirectory can be created, otherwise throw ValidationException

sibling PR related to issue jenkinsci/cucumber-reports-plugin#213: #717

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@f0c78c7). Click here to learn what that means.
The diff coverage is 33.33%.

@@            Coverage Diff            @@
##             master     #718   +/-   ##
=========================================
  Coverage          ?   98.02%           
  Complexity        ?      448           
=========================================
  Files             ?       45           
  Lines             ?      963           
  Branches          ?       79           
=========================================
  Hits              ?      944           
  Misses            ?        9           
  Partials          ?       10

Impacted Files	Coverage Δ	Complexity Δ
...java/net/masterthought/cucumber/ReportBuilder.java	91.86% <33.33%> (ø)	21 <1> (?)

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[docwhat]

This is pulled out of #693, right? 👍 Good job keeping the author as @AndyGee.

[damianszczepanik]

When this problem could happen? I'm fine with this change as long as I'm convinced that there is no other way to fix the source of the problem

[aravinder111]

@AndyGee Can you provide your input on @damianszczepanik question above ??

I haven't observed this personally, but mkdirs() can return false when it fails to create dirs because of permission level. So throwing an Exception when that happens would be useful.