Change config path to be relative to script

[simaishi]

Changing path to config files to be relative to the vmbuild.rb script, rather than hard-coded /build/config as config dir contains files committed to git, which could be different for different branches

[miq-bot]

Checked commit simaishi@6abc613 with ruby 2.3.3, rubocop 0.47.1, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 0 offenses detected
Everything looks fine. 🍰

[simaishi]

Gaprindashvili backport details:

$ git log -1
commit 69cbc8bef0870a8b73612191271070e2f6581a29
Author: Jason Frey <fryguy9@gmail.com>
Date:   Thu Nov 30 18:42:00 2017 -0500

    Merge pull request #252 from simaishi/fix_config_path
    
    Change config path to be relative to script
    (cherry picked from commit 9f593868900c5d713c7dd601899847a29d525d23)

[simaishi]

Fine backport details:

$ git log -1
commit b7671a4c9759438c884715c6a493ef9e1d9f1982
Author: Jason Frey <fryguy9@gmail.com>
Date:   Thu Nov 30 18:42:00 2017 -0500

    Merge pull request #252 from simaishi/fix_config_path
    
    Change config path to be relative to script
    (cherry picked from commit 9f593868900c5d713c7dd601899847a29d525d23)