Fix gitlab:import:repos Rake task moving repositories into the wrong location

Closes #40765

See merge request gitlab-org/gitlab-ce!15823

(cherry picked from commit 7694ae88)

78f7c3c8 Fix gitlab:import:repos Rake task moving repositories into the wrong location
e8cced80 Fix failing importer test case on MySQL due to missing trailing slash in root path
917a112e Simplify normalizing of paths
86661a3a Use build instead of create in importer spec
f1eaab7b Remove the need for destroy and add a comment in the spec