Complete!

Loaded plugins: fastestmirror

Loading mirror speeds from cached hostfile

* base: mirror.genesisadaptive.com

* extras: mirror.rackspace.com

* updates: mirror.umd.edu

No package kernel-devel-3.10.0-1127.el7.x86_64 available.

Error: Nothing to do

Unmounting Virtualbox Guest Additions ISO from: /mnt

umount: /mnt: not mounted

==> master: Checking for guest additions in VM...

    master: No guest additions were detected on the base box for this VM! Guest

    master: additions are required for forwarded ports, shared folders, host only

    master: networking, and more. If SSH fails on this machine, please install

    master: the guest additions and repackage the box to continue.

    master:

    master: This is not an error message; everything may continue to work properly,

    master: in which case you may ignore this message.

The following SSH command responded with a non-zero exit status.

Vagrant assumes that this means the command failed!

umount /mnt

Stdout from the command:

Stderr from the command:

umount: /mnt: not mounted

Solution:

vagrant plugin uninstall vagrant-vbguest

vagrant plugin install vagrant-vbguest --plugin-version 0.24

Update:   install v0.24.0 and now it is able to install guest additions.

Update2: This bug was introduced in v0.25.0.