MFC r259113, r259115, r259144, r259148:
r259113 (dteske):
Fix failed attempt to send pkg(8) stderr to /dev/null
r259115 (dteske):
Prevent truncating /tmp/bsdinstall_log each time we
exec a module.
r259144 (dteske):
Fix a regression after successfully installing to encrypted
ZFS root, the passphrase is not accepted and a message about
"incorrect key" is displayed.
r259148 (dteske):
Fix a regression resulting in mountroot prompt after attempting
to install to encrypted ZFS root (caused by a typo in a
variable name -- ZFSBOOT_BOOT_FSNAME -> ZFSBOOT_BOOTFS_NAME).
Approved by: re (glebius)
Sponsored by: The FreeBSD Foundation
git-svn-id: svn://svn.freebsd.org/base/releng/10.0@259402
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