[#2037] Make postinstall.sh python one-liners python3 compliant
[#2037] Make postinstall.sh python one-liners python3 compliant

janiheikkinen/irods,janiheikkinen/irods,PaulVanSchayck/irods,janiheikkinen/irods,janiheikkinen/irods,janiheikkinen/irods,janiheikkinen/irods,PaulVanSchayck/irods,PaulVanSchayck/irods,janiheikkinen/irods,PaulVanSchayck/irods,janiheikkinen/irods,PaulVanSchayck/irods,janiheikkinen/irods,PaulVanSchayck/irods,PaulVanSchayck/irods,PaulVanSchayck/irods,PaulVanSchayck/irods