Don't do things that set -e in Travis's shell

Sourcing files that set flags bleed into Travis' wrapper script, which
messes with their workflow, e.g. preventing after_failure scripts from
triggering.

These changes fix that:

* Move exported variables from install.sh to setup.sh, so install.sh
  doesn't have to be sourced.
* Source setup.sh from run.sh, rather than directly from .travis.yml.

In addition, as a good practice, remove `set -e` etc. from setup.sh,
and add a comment not to add them back. It's the sourcing script's
responsibility to set these flags.

scripts/ios/install.sh

@@ -5,7 +5,6 @@ set -o pipefail
 
 mapbox_time "checkout_mason" \
 git submodule update --init .mason
-export PATH="`pwd`/.mason:${PATH}" MASON_DIR="`pwd`/.mason"
 
 mapbox_time "install_xcpretty" \
 gem install xcpretty --no-rdoc --no-ri --no-document --quiet

scripts/ios/run.sh

@@ -4,10 +4,9 @@ set -e
 set -o pipefail
 set -u
 
-BUILDTYPE=${BUILDTYPE:-Release}
+source ./scripts/ios/setup.sh
 
-# Add Mason to PATH
-export PATH="`pwd`/.mason:${PATH}" MASON_DIR="`pwd`/.mason"
+BUILDTYPE=${BUILDTYPE:-Release}
 
 PUBLISH_TAG=($(git show -s --format=%B | sed -n 's/.*\[publish \([a-z]\{1,\}\)-v\([0-9.]\{1,\}\)\].*/\1 \2/p'))
 PUBLISH_PLATFORM=${PUBLISH_TAG[0],-}

scripts/ios/setup.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# This script is sourced; do not set -e or -o pipefail here.
+
+# Ensure mason is on the PATH
+export PATH="`pwd`/.mason:${PATH}" MASON_DIR="`pwd`/.mason"