upload: re-allow white space in filenames

upload: re-allow white space in filenames

Some fields (e.g. filename) can contain spaces, but our 'trim'
function, would only return the value until the first whitespace
character instead of removing leading/trailing white space. This lead
to passing the wrong filename to the API call (e.g. 'foo' instead of
'foo (1).iso'), which would then reject it because of the 'wrong'
extension.

Fix this by just using the battle proven trim from pve-common.

Fixes: 0fbcbc2 ("fix #3990: multipart upload: rework to fix uploading small files")
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>