sshd_installer.conf: be more strict on sshpassword= identification

Suggested-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Signed-off-by: Yann Dirson <yann.dirson@vates.fr>

Author: ydirson

startup/sshd_installer.conf

@@ -2,4 +2,4 @@
 ConditionKernelCommandLine=sshpassword
 
 [Service]
-ExecStartPre=/bin/sh -c '/bin/sed -e "s/.*sshpassword=\([^ ]*\).*/root:\1/" /proc/cmdline | /sbin/chpasswd'
+ExecStartPre=/bin/sh -c '/bin/sed -e "s/.*\<sshpassword=\([^ ]*\).*/root:\1/" /proc/cmdline | /sbin/chpasswd'