bootstrap: use bash on illumos to run install scripts
bootstrap: use bash on illumos to run install scripts

The default illumos shell ("sh" in the default PATH) is ksh93, rather
than bash, and does not support constructs like "local" that came from
bash.  The bootstrap function for invoking "install.sh" scripts should
use "bash" explicitly there to avoid issues.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust