fix #1844: check /etc/.pve-ignore.hosts early

fix #1844: check /etc/.pve-ignore.hosts early

Our checks for .pve-ignore.* files happen at write time so
we mostly don't have to think about them within the
functions dealing with them. /etc/hosts is one of the files
we need nowhere except when updating it, and there are some
tools managing it and producing files too large for our
default file_get_contents() size limit, so here we want to
skip early to avoid an error at read time.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>