terminal: disable zsh support when running under flatpak
@chergert
Submitted by Christian Hergert Link to original bug (#780336)
Description
Zsh tries to communicate (improperly) with other sessions, and seems to discover them using the ipc namespace. This causes problems since our PTY are in a different mount namespace and alternate pts mount.
When running under flatpak, this is problematic because the zsh sessions will want to communicate, but they will not be able to find the right ptsname as it is in the mount namespace.
Alternatively, if we can pass an option to zsh to prevent it from IPC'ing between sessions, that would preferred.