hostcfgd passwd_aging_expire_modify always logs error even when chage succeeds

[b39b332d]

Description

In PasswHardening.passwd_aging_expire_modify(), a spurious error is always logged to
syslog on every invocation — even when chage executes successfully.

Steps to reproduce

1. Configure password hardening policy with expiration days in CONFIG_DB
2. Observe syslog output

Actual behavior

Syslog always contains the following error regardless of whether chage succeeded:

Suggested fix

Replace Popen + poll() with wait() to block until the child process exits, then
check the actual return code:

chage_p_m = subprocess.Popen(
    ('chage', chage_flag + str(curr_expiration), normal_account),
    stdout=subprocess.PIPE,
    stderr=subprocess.PIPE
)
chage_p_m.wait()
return_code_chage_p_m = chage_p_m.returncode
if return_code_chage_p_m != 0:
    syslog.syslog(syslog.LOG_ERR, "failed: return code - {}".format(return_code_chage_p_m))

[dlanov]

Hi, I would like to work on this. I plan a minimal fix that waits for the chage process to finish before checking its return code, with focused unit tests for both successful and failed execution.