Honor /etc/fstab in Filesystem.Mount
Documentation for http://storaged.org/doc/udisks2-api/latest/gdbus-org.freedesktop.UDisks2.Filesystem.html#gdbus-method-org-freedesktop-UDisks2-Filesystem.Mount says:
The directory the filesystem will be mounted in is determined by looking at data related to the device or filesystem (such the filesystem UUID and label) and will be created automatically except if the device the filesystem resides on is referenced in the /etc/fstab file
If the device in question is referenced in the /etc/fstab file, the mount command is called directly (as root) and the given options or filesystem type given in options are ignored.