move bash flag to set statement (#3494)

Passing bash with flags to the first argument of /usr/bin/env requires
its own flag to interpret it correctly.  Rather than use `env -S` to
split the argument, have the script `set -e` to enable the same behavior
explicitly in preinst and postinst scripts.

Also set `-o pipefail` for consistency.

Closes: #3492

Signed-off-by: Cole White <cwhite@wikimedia.org>
(cherry picked from commit 2fbf335)

buildSrc/src/main/resources/deb/postinst.ftl

@@ -1,2 +1,3 @@
-#!/usr/bin/env bash -e
+#!/usr/bin/env bash
+set -e -o pipefail
 <% commands.each {command -> %><%= command %><% } %>

buildSrc/src/main/resources/deb/preinst.ftl

@@ -1,2 +1,3 @@
-#!/usr/bin/env bash -e
+#!/usr/bin/env bash
+set -e -o pipefail
 <% commands.each {command -> %><%= command %><% } %>