Fix testing of ibft attribute on device.
Fix for the [bug
1164195](https://bugzilla.redhat.com/show_bug.cgi?id=1164195) was pushed
already but with an issue. When I used iscsi with ibft I have found that I can't add
`/boot` on iscsi drive with `ip=ibft` set.
*Related: rhbz#1164195*
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To view this pull request on github, visit
https://github.com/rhinstaller/anaconda/pull/169