Use binary locations in if statements

[sveeke]

Serverbot now uses something like:

if [ "$(command -v dnf)" ]; then
    ...
fi

While it might be better to just check the location of the binaries:

if [ -f "/usr/bin/dnf" ]; then
    ...
fi

Examples:
if [ -f "/usr/bin/yum" ]; then
if [ -f "/usr/bin/dnf" ]; then
if [ -f "/usr/bin/apt-get" ]; then
if [ -f "/usr/bin/apk" ]; then
if [ -f "/usr/bin/pacman" ]; then
if [ -f "/etc/init.d/sshd" ]; then
if [ -f "/etc/init.d/ssh" ]; then
if [ -f "/etc/rc.d/sshd" ]; then