If user specifies we should create an LV as a cached LV, we need to transform
the parameters in to a CacheRequest instance and pass it to blivet to create a
new LV as cached.
This PR requires the [blivet's PR #190]
(
https://github.com/rhinstaller/blivet/pull/190) to be merged first and the appropriate
bump of the required version of blivet will be done before this gets pushed.
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To view this pull request on github, visit
https://github.com/rhinstaller/anaconda/pull/264