Reduce disk usage of IceTray Runner

[RasmusOrsoe]

This PR solves #861 by adding --no-cache-dir to pip installation commands. By using this optional argument, pip does not store wheels after installation, freeing up multiple gb's of space.

Additionally, the PR adds another print statement of diskusage to the workflow for future debugging. Below is the usage before and after installation for reference.

Before installation

Filesystem      Size  Used Avail Use% Mounted on
overlay          73G   63G   11G  87% /
tmpfs            64M     0   64M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/root        73G   63G   11G  87% /__t
tmpfs           3.2G  1.3M  3.2G   1% /run/docker.sock
tmpfs           7.9G     0  7.9G   0% /proc/acpi
tmpfs           7.9G     0  7.9G   0% /proc/scsi
tmpfs           7.9G     0  7.9G   0% /sys/firmware

After installation

Filesystem      Size  Used Avail Use% Mounted on
overlay          73G   69G  3.9G  95% /
tmpfs            64M     0   64M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/root        73G   69G  3.9G  95% /__t
tmpfs           3.2G  1.3M  3.2G   1% /run/docker.sock
tmpfs           7.9G     0  7.9G   0% /proc/acpi
tmpfs           7.9G     0  7.9G   0% /proc/scsi
tmpfs           7.9G     0  7.9G   0% /sys/firmware

closes #861

[Aske-Rosted]

Looks good, nice with the additional information about the available space for the future.