Agent: Check for spaces in IP or domain names

socket.gethostbyname() may return different results on different systems
when provided with an IP address that contains a space. This depends on
python version or other environmental factors. For example:

System 1:
>>> socket.gethostbyname('172.60 .9.109')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
socket.gaierror: [Errno -2] Name or service not known
>>> socket.gethostbyname('172.17 .9.109')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
socket.gaierror: [Errno -2] Name or service not known

System 2:
>>> socket.gethostbyname('172.60 .9.109')
'172.0.0.60'

To remedy this, this commit adds a check to verify that the IP/domain
does not contain a space, as a space is an illegal character in either.

monkey/common/network/network_range.py

@@ -192,6 +192,9 @@ class SingleIpRange(NetworkRange):
         # The most common use case is to enter ip/range into "Scan IP/subnet list"
         domain_name = None
 
+        if " " in string_:
+            raise ValueError(f'"{string_}" is not a valid IP address or domain name.')
+
         # Try casting user's input as IP
         try:
             ip = ipaddress.ip_address(string_).exploded