debos sometimes fails to mount things

Description

I’ve encountered at least two jobs where build failed because of a failed mount:

Job 497981:

[  OK  ] Reached target Local File Systems (Pre).
         Mounting /builds/infrastructure/apertis-image-recipes...
         Mounting /scratch...
         Mounting /run/fakemachine...
         Mounting /etc/alternatives...
         Mounting /etc/dbus-1...
         Mounting /var/lib/binfmts...
         Mounting /etc/ssl...
[  OK  ] Mounted /builds/infrastructure/apertis-image-recipes.
[  OK  ] Mounted /scratch.
[  OK  ] Mounted /run/fakemachine.
[  OK  ] Mounted /etc/alternatives.
         Mounting /builds/infrastru…ertis-image-recipes/scripts...
         Mounting /builds/infrastru…ertis-image-recipes/keyring...
         Mounting /builds/infrastru…20201030.1232/amd64/sysroot...
[  OK  ] Started udev Kernel Device Manager.
[  OK  ] Mounted /etc/dbus-1.
[  OK  ] Mounted /var/lib/binfmts.
[  OK  ] Mounted /etc/ssl.
[FAILED] Failed to mount /builds/in…apertis-image-recipes/scripts.
See 'systemctl status "builds-infrastru…x2drecipes-scripts.mount"' for details.
[DEPEND] Dependency failed for Local File Systems.
[  OK  ] Mounted /builds/infrastruc…apertis-image-recipes/keyring.
[  OK  ] Mounted /builds/infrastruc…a/20201030.1232/amd64/sysroot.
…
You are in emergency mode. After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" or "exit"
to boot into default mode.
Give root password for maintenance
(or press Control-D to continue): 

Another one is job 498150, this time with a different mountpoint:

[  OK  ] Reached target Local File Systems (Pre).
         Mounting /etc/dbus-1...
         Mounting /scratch...
         Mounting /var/lib/binfmts...
         Mounting /etc/alternatives...
         Mounting /builds/infrastructure/apertis-image-recipes...
         Mounting /run/fakemachine...
         Mounting /etc/ssl...
[  OK  ] Started udev Coldplug all Devices.
[  OK  ] Mounted /etc/dbus-1.
[  OK  ] Mounted /scratch.
[  OK  ] Mounted /var/lib/binfmts.
[  OK  ] Mounted /etc/alternatives.
[  OK  ] Mounted /builds/infrastructure/apertis-image-recipes.
[  OK  ] Mounted /run/fakemachine.
         Mounting /builds/infrastru…20201030.1251/amd64/minimal...
         Mounting /builds/infrastru…ertis-image-recipes/scripts...
         Mounting /builds/infrastru…ertis-image-recipes/keyring...
[  OK  ] Started udev Kernel Device Manager.
[  OK  ] Mounted /etc/ssl.
[FAILED] Failed to mount /builds/in…a/20201030.1251/amd64/minimal.
See 'systemctl status "builds-infrastru…1251-amd64-minimal.mount"' for details.
[DEPEND] Dependency failed for Local File Systems.
[  OK  ] Mounted /builds/infrastruc…apertis-image-recipes/scripts.
         Starting Enable support fo…l executable binary formats...
[  OK  ] Stopped Dispatch Password …ts to Console Directory Watch.
[  OK  ] Reached target Sockets.
[  OK  ] Reached target Timers.
[  OK  ] Started Emergency Shell.
[  OK  ] Reached target Emergency Mode.
         Starting Create Volatile Files and Directories...
         Starting Network Service...
[  OK  ] Mounted /builds/infrastruc…apertis-image-recipes/keyring.
[  OK  ] Started Create Volatile Files and Directories.
[src/bin/slirp-seq.rs:90] "New connection" = "New connection"
[  OK  ] Started Network Service.
random: crng init done
You are in emergency mode. After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" or "exit"
to boot into default mode.
Give root password for maintenance
(or press Control-D to continue): 

Management data

This section is for management only, it should be the last one in the description.

Phabricator link: https://phabricator.apertis.org/T7512