Ensure mounted nfs filesystems matches their fstab declared counterpart

Summary:
When a nfs fs is declared in /etc/fstab and the filesystem path ends with a / (like 192.168.1.16:/home/meven/ ), once mounted the detected filesystem path does not have the slash.
This causes the mounted drive not to match the umounted filesystem, causing the later bug.

I.e :

$ solid-hardware list
[...]
udi = '/org/kde/fstab/192.168.1.16:/home/meven/' (fstab declared mount)
udi = '/org/kde/fstab/192.168.1.16:/home/meven' (mounted drive as returned by getmntent)

The patch makes the logic in Solid::Backends::Fstab::FstabHandling::deviceList matching mounted and unmounted filesytems unsensitive to their path ending with /

BUG: 406242
CCBUG: 390691
FIXED-IN: 5.66

Test Plan:
Locally tested with Linux with a nfs drive set up with a path ending with a slash like
192.168.1.16:/home/meven/ /media/NFS nfs defaults,user,auto,noatime,bg 0 0

After patch
$ solid-hardware list
[...]
udi = '/org/kde/fstab/192.168.1.16:/home/meven' (mounted drive as returned by getmntent)

Only one icon appears for the drive in places panel in Dolphin.

Not tested with getmntinfo / BSD code path, but the patch does not alter the code behavior much and don't foresee any risk there.

Reviewers: bruns, Frameworks, ngraham

Reviewed By: bruns, ngraham

Subscribers: broulik, dhaumann, anthonyfieroni, ngraham, bruns, apol, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D21204