Handle cases where dependencies are missing

[jamesmcm]

If wireguard-tools or openvpn are missing then warn the user and handle error from std::Process.

Make them mandatory in AUR packages, and add dependencies to README for other distros (Debian, Fedora, etc.)

[jamesmcm]

Done in #13

[joelpet]

Make them mandatory in AUR packages, and add dependencies to README for other distros (Debian, Fedora, etc.)

This part does not seem to be done. Here's what the currently most recent Debian package looks like on my machine (notice the lack of Depends: wireguard-tools):

Package: vopono
Version: 0.6.3
Status: install ok installed
Priority: optional
Maintainer: James McMurray <[email protected]>
Installed-Size: 8,183 kB
Homepage: https://github.com/jamesmcm/vopono
Vcs-Browser: https://github.com/jamesmcm/vopono
Vcs-Git: https://github.com/jamesmcm/vopono
Standards-Version: 3.9.4
Download-Size: unknown
APT-Manual-Installed: yes
APT-Sources: /var/lib/dpkg/status
Description: Launch applications via VPN tunnels using temporary network namespaces

Here's what I get when running vopono exec ....

 2020-12-20T17:57:47.382Z ERROR vopono::wireguard > wg binary not found. Is wireguard-tools installed and on PATH?
Error: wg binary not found. Is wireguard-tools installed and on PATH?: CannotFindBinaryPath

One could argue that the dependency on wireguard-tools should be optional as the vopono sync operation is useful in itself.

[jamesmcm]

Yeah, it's only done on the AUR.

I'll add the dependencies to the cargo-deb file: https://github.com/mmstick/cargo-deb