[NEXUS-7596] Only activate Yum capabilities if create/mergerepo are available

commit 0e487008eb2ae646c53d5e5bcc01a48580535252
Merge: af44205 c382117
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Fri Oct 24 10:23:22 2014 +0300

    Merge remote-tracking branch 'origin/nexus-2.11.x' into nexus-2.11.x-NEXUS-7596-check-createrepo

    Conflicts:
    	plugins/yum/nexus-yum-repository-plugin/src/main/java/org/sonatype/nexus/yum/internal/task/MergeMetadataTask.java

commit af44205ca6ed36f70eed7372d652ddcb6ee4623f
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Thu Oct 23 22:12:55 2014 +0300

    [NEXUS-7596] Add @Nullable / JavaDoc

commit e23251b6a7edec38d755c6f702e93c4dfeee37d3
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 23:20:13 2014 +0300

    [NEXUS-7596] Tidy

commit 7621c9e753048e94d2e4590177bdd6408e8deb95
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 23:17:42 2014 +0300

    [NEXUS-7596] Remove wrong activation condition

commit f7bd8c6e64113acecfcf6bc82f3628b40fc15163
Merge: 2e4b74c aeee5a0
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 23:12:31 2014 +0300

    Merge remote-tracking branch 'origin/nexus-2.11.x' into nexus-2.11.x-NEXUS-7596-check-createrepo

    Conflicts:
    	plugins/yum/nexus-yum-repository-plugin/src/main/java/org/sonatype/nexus/yum/internal/task/GenerateMetadataTask.java

commit 2e4b74c3f773d7edd8a6bbd20ab291815754e4a6
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 23:07:32 2014 +0300

    [NEXUS-7596] Tidy

commit 906a2250fb4c6daa2eef70433e0f410941f1a871
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 23:06:40 2014 +0300

    [NEXUS-7596] Validate detected create/mergerepo version

commit 1bb30816e64f658e72994a46cd9856eccd2c47ea
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 21:19:04 2014 +0300

    [NEXUS-7596] Add optional paths to create/mergerepo

commit 3d301f3613f6e339c72d82cef48a7b3b94593ee3
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Mon Oct 20 15:52:16 2014 +0300

    [NEXUS-7596] Only activate Yum capabilities if create/mergerepo are available