Add /etc/terminfo to the terminfo search paths
auto merge of #12656 : Armavica/rust/terminfo, r=sfackler

According to `/etc/terminfo/README`,
```
This directory is for system-local terminfo descriptions. By default,
ncurses will search ${HOME}/.terminfo first, then /etc/terminfo (this
directory), then /lib/terminfo, and last not least /usr/share/terminfo.
```