Check for user being a system user is incorrect

The code here checks /etc/login.defs to see if the user's UID is less than UID_MIN.

However, login.defs also has settings to defined min/max SYSTEM UID range:

```
# System accounts
SYS_UID_MIN 201
SYS_UID_MAX 999
```

In our use case, this causes problems because the admin ID is created very early in provisioning BEFORE we can set our standard values for UID_MIN / UID_MAX... and after we do, then the admin ID falls outside the range and is marked as a system user.

The check would be better to also validate against SYS_UID_MAX.

```
uid_min = None
try:
uid_min = int(ext_utils.get_line_starting_with("UID_MIN", "/etc/login.defs").split()[1])
except (ValueError, KeyError, AttributeError, EnvironmentError):
pass
if uid_min is None:
uid_min = 100
if user_entry is not None and user_entry[2] < uid_min:
logger.error(
"CreateAccount: " + user + " is a system user. Will not set password.")
return "Failed to set password for system user: " + user + " (0x06)."

```
https://github.com/Azure/azure-linux-extensions/blob/b4d783a87157675f81505aa94af5bb2935a1307d/Utils/distroutils.py#L175

Start in Utils/distroutils.py around the user check linked in the issue, and read how /etc/login.defs values are parsed. Verify the system-user decision against the documented UID ranges, including SYS_UID_MAX, and confirm that an early-provisioned admin is no longer misclassified.

Written by the indexing model from the issue text.