initramfs and noexec /tmp

If during creation of new initramfs by update-initramfs (called by e.g.
kernel postinst script) /tmp is mounted with 'noexec', initramfs will be
slightly different and may report errors, like

E: /scripts/local-premount/resume failed with return 255.

shell's 'errexit' option and variable definition.

Shell's option 'errexit' works unexpectedly when command returning non-zero
is called in `local` variable definition statement.