Add tests for print().

test/box/print.result

+print("Hello, world")
+---
+...
+box.fiber.wrap(function() print("Hello, world") end)
+---
+- null
+...
+box.fiber.sleep(0.1)
+---
+...
+Check log line
+---
+- "line contains 'Hello'" 
+...
+box.fiber.wrap(function() print("Ehllo, world") end)
+---
+- null
+...
+box.fiber.sleep(0.1)
+---
+...
+Check log line
+---
+- "line doesn't contain 'Hello'" 
+...
+box.fiber.wrap(function() print() end)
+---
+- null
+...
+box.fiber.sleep(0.1)
+---
+...
+Check log line
+---
+- "line doesn't contain 'PPPPPPPP'" 
+...

test/box/print.test.py

+import tarantool
+
+import sys
+import os
+import re
+
+
+admin('print("Hello, world")')
+
+log = os.path.join(vardir, "tarantool.log")
+f = open(log, "r")
+f.seek(0, 2)
+
+admin('box.fiber.wrap(function() print("Hello, world") end)')
+admin('box.fiber.sleep(0.1)')
+line = f.readline()
+print("Check log line")
+print("---")
+if re.search('(Hello)', line).start(1) > 0:
+    print("""- "line contains 'Hello'" """)
+    print("...")
+
+admin('box.fiber.wrap(function() print("Ehllo, world") end)')
+admin('box.fiber.sleep(0.1)')
+line = f.readline()
+print("Check log line")
+print("---")
+if re.search('(Hello)', line):
+    print("""- "line contains 'Hello'" """)
+else:
+    print("""- "line doesn't contain 'Hello'" """)
+print("...")
+
+admin('box.fiber.wrap(function() print() end)')
+admin('box.fiber.sleep(0.1)')
+line = f.readline()
+print("Check log line")
+print("---")
+if re.search('(PPPPPPPP)', line):
+    print("""- "line contains 'PPPPPPPP'" """)
+else:
+    print("""- "line doesn't contain 'PPPPPPPP'" """)
+print("...")