reproducible osuosl174: Default to using tmpfs /tmp for schroots.

This machine has plenty of ram and it allows multiple sbuild runs
concurrently with the same build path.

hosts/osuosl174-amd64/etc/schroot/default/fstab

+# fstab: static file system information for chroots.
+# Note that the mount point will be prefixed by the chroot path
+# (CHROOT_PATH)
+#
+# <file system> <mount point>   <type>  <options>       <dump>  <pass>
+/proc           /proc           none    rw,bind         0       0
+/sys            /sys            none    rw,bind         0       0
+/dev            /dev            none    rw,bind         0       0
+/dev/pts        /dev/pts        none    rw,bind         0       0
+/home           /home           none    rw,bind         0       0
+tmpfs           /tmp        tmpfs   defaults        0       0
+
+# It may be desirable to have access to /run, especially if you wish
+# to run additional services in the chroot.  However, note that this
+# may potentially cause undesirable behaviour on upgrades, such as
+# killing services on the host.
+#/run           /run            none    rw,bind         0       0
+#/run/lock      /run/lock       none    rw,bind         0       0
+/dev/shm       /dev/shm        none    rw,bind         0       0
+/run/shm       /run/shm        none    rw,bind         0       0
+
+
+# jenkins-specific stuff:
+# <file system> <mount point>   <type>  <options>       <dump>  <pass>
+/srv/reproducible-results /srv/reproducible-results none rw,bind 0 0
+/srv/d-i        /srv/d-i        none    rw,bind         0        0
+/srv/jenkins    /srv/jenkins    none    rw,bind         0        0