Download dependencies over http, not https

libcurl bundled with cmake doesn't support https. To enable building
sysdig without libcurl installed system wide, we need to replace
the https URLs with http.

The files still have their checksums verified.

Author: gnosek

CMakeLists.txt

@@ -435,7 +435,7 @@ if(NOT WIN32 AND NOT APPLE)
 		set(CARES_INCLUDE "${CARES_SRC}/target/include")
 		set(CARES_LIB "${CARES_SRC}/target/lib/libcares.a")
 		ExternalProject_Add(c-ares
-		URL "https://download.sysdig.com/dependencies/c-ares-1.13.0.tar.gz"
+		URL "http://download.sysdig.com/dependencies/c-ares-1.13.0.tar.gz"
 		URL_MD5 "d2e010b43537794d8bedfb562ae6bba2"
 		CONFIGURE_COMMAND ./configure --prefix=${CARES_SRC}/target
 		BUILD_COMMAND ${CMD_MAKE}
@@ -462,7 +462,7 @@ if(NOT WIN32 AND NOT APPLE)
 		set(PROTOBUF_LIB "${PROTOBUF_SRC}/target/lib/libprotobuf.a")
 		ExternalProject_Add(protobuf
 		DEPENDS openssl zlib
-		URL "https://github.com/google/protobuf/releases/download/v3.5.0/protobuf-cpp-3.5.0.tar.gz"
+		URL "http://github.com/google/protobuf/releases/download/v3.5.0/protobuf-cpp-3.5.0.tar.gz"
 		URL_MD5 "e4ba8284a407712168593e79e6555eb2"
 		# TODO what if using system zlib?
 		CONFIGURE_COMMAND /usr/bin/env CPPFLAGS=-I${ZLIB_INCLUDE} LDFLAGS=-L${ZLIB_SRC} ./configure --with-zlib --prefix=${PROTOBUF_SRC}/target