Consider '-o pipefail' for default bash

[mkpankov]

Code like

          curl -fL https://getcli.jfrog.io | sh
          jfrog rt download sdk/StarterKit-001/*

Doesn't fail on first line when curl is missing:

  ciri-dev-5 git:(vagga) ✗ vagga _build jfrog
+ curl -fL https://getcli.jfrog.io
/bin/sh: 1: curl: not found
+ sh
+ jfrog rt download sdk/StarterKit-001/*
/bin/sh: 2: jfrog: not found
ERROR 2019-06-28T15:44:36Z: vagga::builder: Error building container "jfrog": step Sh("curl -fL https://getcli.jfrog.io | sh\njfrog rt download sdk/StarterKit-001/*\n") failed: Error running <Command "/bin/sh" "-exc" "curl -fL https://getcli.jfrog.io | sh\njfrog rt download sdk/StarterKit-001/*\n"; environ[8]; chroot="/vagga/root"; work-dir="/work">: exited with code 127
ERROR 2019-06-28T15:44:36Z: vagga::wrapper: Error executing _build: Builder exited with code 1
Command <Command "/proc/self/exe" "__wrapper__" "_build" "jfrog"; environ[6]; uid_map=[UidMap { inside_uid: 0, outside_uid: 1000, count: 1 }, UidMap { inside_uid: 1, outside_uid: 100000, count: 65535 }]; gid_map=[GidMap { inside_gid: 0, outside_gid: 1000, count: 1 }, GidMap { inside_gid: 1, outside_gid: 100000, count: 65535 }]> exited with code 124