Device certificates are created with extra permissions

After pki/create-thing-creds.sh creates IoT device certificate it contains extra privileges:
```
X509v3 Basic Constraints: critical
CA:TRUE, pathlen:2
```
and
```
X509v3 Key Usage: critical
Digital Signature, Certificate Sign, CRL Sign
```

It should be
```
X509v3 Basic Constraints: critical
CA:FALSE
```
and
```
X509v3 Key Usage: critical
Digital Signature
```

I think it because wrong int1CA.cnf is used in the command:
```
openssl ca -batch -config int1CA.cnf -extensions v3_req -days 365 -md sha256 -in ../devices/$THING_NAME.csr.pem -out ../devices/$THING_NAME.crt.pem
```

Solution: provide another openssl configuration file to generate certificate for a device. That config file should miss CA:TRUE and Certificate Sign, CRL Sign rights.

Start in pki/create-thing-creds.sh and inspect the openssl ca command that uses int1CA.cnf with the v3_req extension. Add or select a device certificate configuration that produces CA:FALSE and only Digital Signature, then verify the generated certificate's Basic Constraints and Key Usage with the displayed certificate inspection command.

Written by the indexing model from the issue text.