I previous was on JunOS 17.4R1 & now I tested on ex9204 running junos 17.1R2.7 same as yours & get option of power-off/halt. Could you get "show chassis hardware" & "show configuration system" from your box?
labroot@EX9200-SW1> request system ?
Mar 14 19:42:09
Possible completions:
certificate Manage X509 certificates
commit Perform commit related operations
configuration Request operation on system configuration
decrypt Decrypt a $8$ or $9$-encrypted password
halt Halt the system
license Manage feature licenses
logout Forcibly end user's CLI login session
personality-file Execute commands related to personality of a device
power-off Power off the software on RE
power-on Power on the system
process Request operation on system process
reboot Reboot the system
recover Recover a specified volume
scripts Manage scripts (commit, op, event)
snapshot Create a normal Junos or a recovery snapshot
software Perform system software extension or upgrade
storage Request operation on system storage
yang Perform YANG schema operations
zeroize Erase all data, including configuration and log files
labroot@EX9200-SW1> show version
Mar 14 19:43:32
Hostname: EX9200-SW1
Model: ex9204
Junos: 17.1R2.7
JUNOS OS Kernel 64-bit [20170607.351421_builder_stable_10]
JUNOS OS libs [20170607.351421_builder_stable_10]
JUNOS OS runtime [20170607.351421_builder_stable_10]
JUNOS OS time zone information [20170607.351421_builder_stable_10]
JUNOS OS libs compat32 [20170607.351421_builder_stable_10]
JUNOS OS 32-bit compatibility [20170607.351421_builder_stable_10]
JUNOS py extensions [20170617.054345_builder_junos_171_r2]
JUNOS py base [20170617.054345_builder_junos_171_r2]
JUNOS OS crypto [20170607.351421_builder_stable_10]
JUNOS network stack and utilities [20170617.054345_builder_junos_171_r2]
JUNOS modules [20170617.054345_builder_junos_171_r2]
JUNOS mx modules [20170617.054345_builder_junos_171_r2]
JUNOS libs [20170617.054345_builder_junos_171_r2]
JUNOS libs compat32 [20170617.054345_builder_junos_171_r2]