As files in the store and /etc/fstab are world readable, specifying the
password in the file-system record is suboptimal. To mitigate this,
`mount.cifs' supports reading `username', `password' and `domain' options from
a file named by the `credentials' or `cred' option.
* gnu/build/file-systems.scm (mount-file-system): Read mount options from the
file specified via the `credentials' or `cred' option if specified.
Change-Id: I786c5da373fc26d45fe7a876c56a8c4854d18532
Signed-off-by: Ludovic Courtès <ludo@gnu.org>